Currently there is no way to determine how many customers should be provisioned on a router by a service provider implementing Virtual Private Network (VPN) services. If too many customers are assigned to a router, the required memory will exceed the router memory, and extra routers must be deployed. The expected commercial benefit is cost reduction. A fully loaded Cisco GSR router costs nearly $1 Million after all the financial loading which includes: office engineering and installation.
Each router with an interface for a VPN must store the entire routing table for that VPN. The largest VPNs consume about 5% of the memory on a Cisco GSR router to which the VPN is assigned. Avoiding having to provision a VPN on two routers can thus save 5% of the memory on the second router which translates to a 5% reduction of the cost of a $1 million router or $50,000. If there are 30 locations and the largest VPN can be provisioned on only one router in the 30 locations, the savings for this VPN alone can be estimated as (30) ($50,000) or $1.5 Million. Saving memory means saving money.
There is a need for a method of determining how many customers can be assigned to a router so that with a high probability the assigned VPNs will not exceed the router's memory.